Resampling procedures to compare two survival distributions in the presence of right-censored data

In this simulation study. the accuracy of the size of four classes of test procedures-asymptotic normal test, permutation test, bootstrap hypothesis test, and bootstrap interval test-were compared using the logrank and Prentice-Wilcoxon two sample test statistics. Sample sizes of 20 and 50 per group were used. Twenty observations per group yielded differences in the test procedures. When the Prentice-Wilcoxon test statistic was employed, the asymptotic test procedure was the most accurate; resampling procedures did not improve upon its accuracy. Using the logrank test statistic, the permutation or bootstrap hypothesis testing procedures were closest to the nominal significance level. The more popular asymptotic normal logrank test was consistently anticonservative. When the number of observations in each group was increased to 50, the test procedures were comparable. Power comparisons were also examined. The test with the greatest power was dependent upon the two survival patterns and the choice of test statistic.